A common-rail fuel injection system that leaks a part of a high-pressure fuel supplied to an injector to a low-pressure side is known as a type of common-rail fuel injection system.
Since a leakage quantity to the low-pressure side in the injector affects a pressure of the high-pressure fuel supplied to the injector, it consequently constitutes a factor of varying an actual injection quantity from the injector.
The injector is fabricated so that its leakage quantity falls within a predefined range.
As a conventional common-rail fuel injection system, the following common-rail fuel injection system is known. A leakage quantity in an injector is estimated in a control device from a speed of revolution of a supply pump (generally, a speed of revolution of an engine), a temperature of a fuel supplied to the injector, a pressure of a common rail (hereinafter, referred to as a common-rail pressure) and the like. An injection quantity from the injector is corrected by the control device based on the estimated leakage quantity (for example, see Japanese Patent Laid-Open Publications Nos. 2000-18068 and 2000-257478).
(Drawbacks in the Conventional Techniques)
In the conventional techniques, the leakage quantity is estimated from an operating state (the speed of revolution of the supply pump, the fuel temperature, the common-rail pressure, and the like) while a basic leakage quantity of the injector itself is being kept constant. Therefore, a fluctuation in the basic leakage quantity caused by the change of the injector with elapse of time, for example, injector wear and the like has not been taken into consideration. Specifically, the conventional common-rail fuel injection systems do not have any means of detecting a fluctuation in the basic leakage quantity caused by the change of the injector with elapse of time.
As described above, the conventional common-rail fuel injection systems do not have any means of detecting a fluctuation in the basic leakage quantity generated by the change of the injector with elapse of time. Therefore, when the basic leakage quantity of the injector itself increases as indicated with a solid line A in FIG. 3 due to the change of the injector such as wear of a sliding part or a closed part with elapse of time, a fuel pressure applied to a nozzle of the injector decreases. As a result, as indicated with a solid line B in FIG. 3, even if an injection quantity directed by the control device is constant, an actual injection quantity from the injector decreases with the increase in the basic leakage quantity.
Moreover, since the conventional common-rail fuel injection systems do not have means of detecting a fluctuation in the basic leakage quantity generated by the change of the injector with elapse of time, abnormality cannot be detected even when the basic leakage quantity excessively increases.
On the other hand, the injector is fabricated so that the leakage quantity falls within a predefined range as described above. In other words, the leakage quantity varies between injectors within a defined range.
Therefore, in addition to a variation in leakage quantity between injectors, variations between devices such as a variation in other injector elements between injectors, a variation between supply pumps and a variation between pipes are offset by the combination of assembled elements (components and the like). Furthermore, a variation between devices is corrected by the control device so as to obtain specified injection.
As described above, various variations between devices are offset by the combination of assembled elements. Furthermore, the correction is performed so as to obtain specified injection. Therefore, the conventional common-rail fuel injection systems do not have a function of automatically correcting the injection quantity from a median difference in leakage quantity between injectors (a design target value) and a variation in leakage quantity between injectors.